This invention relates to a new and improved method for producing aqueous dispersions of alpha alumina monohydrate and to compositions suitable for forming said dispersions. More specifically, the subject invention comprises a method of readily producing an aqueous dispersion of alpha alumina monohydrate by forming a mixture of alpha alumina monohydrate and water, and subjecting the mixture to high shear rates. The subject invention further comprises forming a composition of alpha alumina monohydrate and an alkali metal oxide, hydroxide or carbonate, forming an aqueous mixture of said composition and subjecting the aqueous mixture to high shear rates for a period of time to form a uniform dispersion.
The ability to homogeneously disperse alpha alumina monohydrate in water is a highly desired object. Aqueous dispersions of alpha alumina monohydrate are required in the formation of extrudates, catalytic monolith surface coatings and aqueous pseudoplastic compositions.
Much effort has been devoted to the development of methods of preparing aqueous dispersions of alpha alumina monohydrate. Conventional manners of producing such dispersions require the utilization of acidic agents. For example, U.S. Pat. No. 3,408,160 to Schmidt et al teaches that one can form alumina slurries by the addition of an acid. Similarly, U.S. Pat. No. 3,357,791 to Napier discloses a method for producing a colloidal dispersion of a monohydrate of aluminum by the addition of about 2.8 weight percent hydrochloric acid based on the alumina monohydrate present. These methods of forming aqueous dispersions are not suitable for certain purposes, such as in the formation of catalytic material due to the required inclusion of a contaminating agent. In other instances the previously known methods are undesirable due to the corrosive nature of the resultant acidic media. Furthermore, the dispersions formed with the aid of an acidic agent do not exhibit the degree of pseudoplasticity required for many applications.